A serum factor which inhibits the stimulation of lymphocytes (LSI) by Epstein-Barr viral antigens was detected in patients with undifferentiated nasopharyngeal carcinoma (NPC). A positive correlation between favorable prognosis and decline of LSI titers was demonstrated. Information was collected relating to the clinical features, pathologic features and hormone receptor status of breast cancer patients in Tunisia. Evidence for the unusual progression of disease in Tunisian breast cancer patients was documented with the finding of a poorer nuclear grade in rapidly progressing breast cancer (RPBC) patients than non-RPBC patients. In contrast to American patients with inflammatory breast cancer, who are reported to have low levels of hormone receptors, patients with RPBC had levels comparable to non-RPBC patients. Information collected on 256 pathologically confirmed cases of Burkitt's lymphoma (BL) diagnosed in the Western Hemisphere demonstrated the curability of BL, particularly in patients with limited disease. Target organs appeared to be related to age, suggesting a predilection of the disease for rapidly dividing cells. Laboratory and epidemiologic studies provided evidence for environmental as well as genetically determined predisposing factors.